The GoogleDoc is updated by pretty much one person who doesn't have a lot of free time, so unfortunately it's often outdated with the boundless amount of data that needs to be entered.
More volunteers would be needed to keep it constantly updated.

Thanks for the information omega64

No pressure, it was just about information :)
When checking it, I saw the creation date, but I could not find a "last updated" info.

Sin Slayers appears to be outdated: GOG installer shows version 1.2.03.1 whereas Steam went further than 1.3.2.9 (although the game is no longer available for purchase on Steam).

Many titles were removed from Steam, lets hope the download will remain cause gamers paid for them.

My favorite HOG development team seems to be inactive or maybe no longer interested in releasing new HOG
on Steam: i have all the HOG from Arttifex Mundi , always bought at release.
The games run without steam which is a plus for me as my steam is not allowed to run at start up :D

Anyway i just don'"t like DRM or any other limitations on games :D.

Just asked about the updates to the Twitter profile @sinslayersgame, which appears to be legit.
Now waiting for a reply.

A new DLC for Door Kickers: Action Squad dropped yesterday on Steam:

https://store.steampowered.com/app/1788610/Professionals_Abroad_DLC/

No gog release as of yet that I can see, so we might want to keep an eye on this.

Here are some of the usual recent releases of games without purchasable bonus DLC:

Defend the Rook is missing the supporter pack DLC
Evertried is missing its soundtrack DLC
Growbot is missing its soundtrack DLC and artbook DLC
They Always Run is missing its soundtrack DLC

EDIT: Evertried's soundtrack can be found DRM-free on Bandcamp:
https://moonsailor.bandcamp.com/album/evertried-original-soundtrack

About Succubus' missing DLCs, a dev announced this earlier today on the team's Discord:

Roki isn't just missing the OST DLC.

On Steam, there's also a deluxe edition that additionally comes with an artbook. The deluxe pack is also available as DLC for the base game, but there's no separate artbook DLC.

Any signs of 2nd class treatment from the new Just Cause games here?

Not really unless you consider a multiplayer mod for a dead game second class. I have no idea who owns the mod even though Steam sells it as DLC but steam clearly market it as a mod.

The devs stated they don't plan to bring it to GOG.

Thank you for sharing. Polygon Treehouse are the type of the developer that can only be reached on social media, so I couldn't ask.

I thought I'd bring it up here so the missing deluxe version/artbook could be mentioned in the Google doc, whenever the curator finds the time.

Wait forget what I said. I was getting Roki mixed up with Tohu.